Onlookers compared the study to the racist psuedoscience of phrenology, which purported that the shape of the skull could reveal character traits.

The academics claimed their results were not psuedoscientific but consistent with the prenatal hormone theory of sexual orientation.

This unproven theory suggests that hormones which people are exposed to in the womb lead to different physiological attributes and also different sexualities.

According to the Google team, however, the algorithm didn't detect a difference in facial features. Instead, it detected a difference in how homosexual and heterosexual men and women take selfies.

"Heterosexual men tend to take selfies from slightly below, which will have the apparent effect of enlarging the chin, shortening the nose, shrinking the forehead, and attenuating the smile," they found.

"This [angle] emphasises dominance - or, perhaps more benignly, an expectation that the viewer will be shorter.

"On the other hand, as a wedding photographer notes in her blog, 'When you shoot from above, your eyes look bigger, which is generally attractive - especially for women.'"

The researchers took photographs of themselves from these different angles to show how they seem to suggest different facial feature.

The analysis by Margaret Mitchell and Blaise Aguera y Arcas from Google, and Alex Todorov from Princeton, concludes: "The obvious differences between lesbian or gay and straight faces in selfies relate to grooming, presentation, and lifestyle - that is, differences in culture, not in facial structure."

So, it turns out that heterosexual men seem to typically take selfies from a lower angle, while heterosexual women take them from a higher angle, because of cultural norms about how we present our own sexuality.